from tkinter import *

root = Tk()

w = Canvas(root,width=400,height=200)
w.pack()

def paint(event):
    x1,y1 = (event.x - 1),(event.y - 1)
    x2,y2 = (event.x + 1),(event.y + 1)
    w.create_oval(x1,y1,x2,y2,fill='red')

w.bind('<B1-Motion>',paint)#绑定鼠标左键

Label(root,text='按住鼠标左键并移动，开始绘制......').pack(side=BOTTOM)#提示标签

mainloop()
